1. Field of the Invention
The present invention relates to an aqueous binder composition based on polyisocyanates and water soluble or water dispersible polyester resins grafted with vinyl monomers and containing carboxylate and hydroxyl groups and a process for the preparation of a coating or sealing composition containing such binder composition.
2. Description of the Prior Art
State of the art two-component polyurethane lacquers have acquired great importance in the coating industry due to their outstanding properties. They have, however, the disadvantage that considerable quantities of organic solvents are required for processing them and these solvents must subsequently be removed, e.g., by combustion. In many applications, especially non-industrial fields of application, such combustion cannot be carried out. Accordingly, there is an increased demand in these fields for coatings which have a high solids content and above all are dilutable in water so that the discharge of solvents and thus environmental pollution can be kept as low as possible.
The use of water as the liquid phase in two-component polyurethane lacquers containing free isocyanate groups is complicated by the fact that isocyanate groups react not only with alcoholic hydroxyl groups but also with water to form urea and carbon dioxide. This generally reduces the pot life, the time available for processing and the quality of the coatings to values which do not meet the practical requirements.
One possible solution is described in DE-OS 3 829 587, in which certain polyhydroxy polyacrylates are combined with polyisocyanates containing free isocyanate groups to form aqueous two-component compositions.
It has now surprisingly been found that special aqueous polyester resins grafted with vinyl monomers and containing carboxylate and hydroxyl groups can be used with polyisocyanates containing free isocyanate groups in aqueous two-component binders.